1. Field of the Invention
The present invention relates to an expanding shoe drum brake and in particular to an expanding shoe drum brake of relatively light weight construction utilizing lift off type, single web brake shoes.
2. Description of the Prior Art
Expanding shoe drum brakes, especially air or hydraulically actuated drum brake systems wherein arcuate brake shoes nonrotatably secured to a portion of a wheeled vehicle are pivotably rotated about an anchor member or members into engagement with a rotating annular brake drum for the purposes of retarding the velocity of the wheeled vehicle by the use of a brake actuating member, such as a displaceable cam element, are well known in the art. The brake actuating member, usually a rotatable cam element or a linear wedge element, is located between the adjacent ends of the pivotal brake shoes and secured to a rotatable cam shaft or a linear actuation shaft, respectively, for translating oscilliatory, generally linear motion from a power source, such as an air motor or the like, to the brake shoes.
The actuating member, often in the form of a so called "S" cam or a wedge, is usually located between cam or wedge followers, often in the form of rollers or the like, rotatably fixed to the brake shoes.
Example of such prior art cam actuated drum brakes may be seen by reference to U.S. Pat. Nos. 3,497,037; 3,096,857 and 2,002,139 all of which are hereby incorporated by reference.
While the prior art cam and/or wedge actuated drum brakes, especially the "S" cam type drum brakes, are well received and accepted, such prior art devices were not totally satisfactory in certain situations as they usually were relatively heavy structures utilizing cast iron parts and multiple web brake shoes to attain the required strength and the required relative alignment between the parts thereof. The prior art has also included various attempts to produce relatively lighter weight cam actuated drum brakes by the utilization of relatively lighter weight stamped components. While many of these lighter weight brake assemblies have been highly satisfactory for certain applications and have been well commercially received, the prior art devices were not totally satisfactory for certain applications, such as for example, in use for a relatively smaller cam actuated drum brake for a front steer or drive steer axle. In particular, the prior art designs have been heavier and/or more complicated than is desired to achieve the required strength of the parts and/or to assure that the brake shoe is properly aligned with the brake drum, especially in the disengaged position of the brake. As is well known, maintaining proper brake shoe and brake drum alignment is desirable for reducing the required running clearance to a minimum and thus preserving the maximum of effective stroke of an air motor or the like. Many of the prior art lighter weight brake assemblies have utilized brake shoes having two or more webs and/or brake shoes having full apertures formed therein in which the anchor member or anchor pin was received in attempts to assure that the brake shoes of the drum brake remained properly aligned with the brake drums thereof.